The invention relates to an exhaust gas recirculation system, for controlling the flow of exhaust gas from an exhaust gas passage to an engine intake passage of an internal combustion engine, and more particularly, to an actuator arrangement for an exhaust gas recirculation system.
Although the use of the present invention is not limited to any particular type of engine, its use is especially advantageous in connection with a diesel engine, for reasons which will become apparent subsequently.
Typically, exhaust gas recirculation (EGR) valves have been disposed between the engine exhaust manifold and the engine intake manifold, and operable, when in the open position, to recirculate exhaust gas from the exhaust side of the engine back to the intake side. As is well known to those skilled in the art, such recirculation of exhaust gases is helpful in reducing various engine emissions.
Many prior art EGR valves have been pressure responsive, and more particularly, have moved between the open and closed positions in response to movement of a diaphragm. One example of such an EGR valve control is shown in U.S. Pat. No. 5,035,228. Normally, the diaphragm is biased by a vacuum signal. However, many vehicles having diesel engines, and requiring EGR systems, do not inherently include a vacuum source. Therefore, the use of a vacuum actuated EGR valve, thus requiring the addition of a vacuum source, would add substantially to the overall cost of the EGR system.
An EGR system including an electrically operated type actuator is illustrated and described in U.S. Pat. No. 5,606,957. The actuator for the valve stem in the cited patent is a stepper motor, which is generally satisfactory in performing the basic function of opening and closing the EGR valve. However, in most vehicle applications for EGR valves, and especially in diesel engine applications, it must be possible to close the EGR valve within 50 milliseconds of the time the closing command is generated, and open the EGR valve within 100 milliseconds of the time the opening command is generated. Thus, the type of stepper motor actuator shown in the cited patent may be able to close the valve quickly enough, but clearly would not be able to open the valve within the required time.